实现pdf中划句子ai伴读的功能，修复pdf高亮显示的问题

addon/content/chatpapers.css

@@ -1038,6 +1038,35 @@ collapsible-section[open] > :not(.head) .chatpapers-lecture-root {
   overflow-y: auto;
 }
 
+.chatpapers-lecture-selection-explain {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+  padding: 10px;
+  border-radius: 8px;
+  background: color-mix(in srgb, #2563eb 6%, transparent);
+  border: 1px solid color-mix(in srgb, #2563eb 18%, transparent);
+  font-size: 12px;
+  line-height: 1.45;
+  max-height: 220px;
+  overflow-y: auto;
+}
+
+.chatpapers-lecture-selection-title {
+  font-size: 12px;
+  font-weight: 700;
+  color: #1d4ed8;
+}
+
+.chatpapers-lecture-selection-replay {
+  align-self: flex-start;
+  margin-top: 4px;
+}
+
+.chatpapers-selection-explain-btn {
+  white-space: nowrap;
+}
+
 .chatpapers-lecture-para-kind {
   font-size: 11px;
   font-weight: 600;

addon/content/icons/pane-adaptive-height-fixed.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="context-stroke" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <!-- Lucide: FoldVertical (adaptive off / fixed height) -->
+  <path d="M12 22v-6"/>
+  <path d="M12 8V2"/>
+  <path d="M4 12H2"/>
+  <path d="M10 12H8"/>
+  <path d="M16 12h-2"/>
+  <path d="M22 12h-2"/>
+  <path d="m15 19-3-3-3 3"/>
+  <path d="m15 5-3 3-3-3"/>
+</svg>

addon/content/icons/pane-adaptive-height.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="context-stroke" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <!-- Lucide: UnfoldVertical (adaptive on) -->
+  <path d="M12 22v-6"/>
+  <path d="M12 8V2"/>
+  <path d="M4 12H2"/>
+  <path d="M10 12H8"/>
+  <path d="M16 12h-2"/>
+  <path d="M22 12h-2"/>
+  <path d="m15 19-3 3-3-3"/>
+  <path d="m15 5-3-3-3 3"/>
+</svg>

addon/content/icons/pane-open-window.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="context-stroke" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <!-- Lucide: AppWindow -->
+  <rect x="2" y="4" width="20" height="16" rx="2"/>
+  <path d="M10 4v4"/>
+  <path d="M2 8h20"/>
+  <path d="M6 4v4"/>
+</svg>